Conversion of carbonaceous materials to synthetic natural gas by pyrolysis, reforming, and methanation

ABSTRACT

The production of synthetic natural gas from a carbonaceous material, preferably a biomass material, such as wood. The carbonaceous material is first pyrolyzed, then subjected to steam reforming to produce a syngas, which is then passed to several clean-up steps then to a methanation zone to produce synthetic natural gas.

CROSS REFERENCE TO RELATED APPLICATIONS

This is based on Provisional Application 60/832803 filed Jul. 24, 2006.

FIELD OF THE INVENTION

The present invention relates to the production of synthetic natural gasfrom a carbonaceous material, preferably a biomass material, such aswood. The carbonaceous material is first pyrolyzed, then subjected tosteam reforming to produce a syngas, which is then passed to severalclean-up steps then to a methanation zone to produce synthetic naturalgas.

BACKGROUND OF THE INVENTION

The world's energy supplies, particularly liquid and gaseous fuel fromfossil fuels, are being depleted faster than they are replaced.Consequently, the development of techniques for producing energy areurgently needed for avoiding the depletion of limited fossil fuelresources as well as for alleviating the global warming problem. Amongvarious types of natural energy, biomass energy is regarded as one ofthe most promising natural energy from the viewpoint of its abundance,renewability and storability. Cellulosic materials, such as wood, havegreat potential for providing large amounts of energy. Direct combustionof woody biomass suffers from a limited amount of resource and lowefficiency, and, further, only electric power can effectively besupplied from the direct combustion of woody biomass. The development oftechniques that can utilize the entire biomass, including cellulose andhemicellulose, to produce energy, particularly in the form of liquid andgaseous fuels is of great interest. At the present time, however, suchtechniques are not in a practical stage for technical as well aseconomical reasons.

There is increasing interest in the production of synthetic natural gasas an alternative to natural gas. Synthetic natural gas, A large portionof synthetic natural gas is often referred to as “green gas” because itis a renewable gas typically obtained from biomass and having naturalgas specifications. Thus, it can be transported through the existingnatural gas infrastructure, substituting for natural gas in all existingapplications. Also, the use of biomass as the feedstock will notgenerally result in a net CO₂ emission as long as the source materialcan be replanted to replace those used as fuel. It may even be possibleto reduce atmospheric CO₂ by sequestering the CO₂ that is releasedduring the conversion of biomass (negative CO₂ emission).

Various problems exist in the art for pyrolyzing or gasifyingcarbonaceous materials, such as cellulosic materials. For example,vessels that have traditionally been used for gasifying biomass, such aswood chips and similar cellulosic material have been cylindrical, oroften wider or narrower at the grate level than at the surface of thefuel bed, relative to the flow of feed and the forced air (or othergases) draft. Concerns with the settling of the fuel bed so thatcombustion takes place without the need to poke or otherwise stir thefuel bed have provoked a variety of vessel construction. None of theselends themselves well to a high volume, precisely controlled, continuousprocess wherein the biomass fuel is efficiently converted to the targetgas for supply to and likely, additional energy or waste in the process.Exposing the base fuel during the pyrolysis to air, water vapor or othercomponents has a direct impact on the products of pyrolysis, as does thetemperature of the process and the duration thereof. By using any of theprocesses of the prior art, such as a fluidized bed, which is, at leastinitially exposed to air and can be additionally exposed to oxygen, orother input gasses, some portion of the fuel for gasification isconsumed, as by oxidation (burning) affecting the output of the processby producing ash or other undesirable residue.

Although several prior processes have met with varying degrees of bothcommercial and technical success, there is still a need in the art forimproved and more efficient processes for converting biomass tosynthetic natural gas.

SUMMARY OF THE INVENTION

In accordance with the present invention there is provided a process forconverting carbonaceous material to synthetic natural gas, which processcomprising:

a) feeding said carbonaceous material and an effective amount ofsuperheated steam in a plurality of vertically oriented straight tubesin a pyrolysis furnace, which tubes are at a temperature of about 400°C. to about 650° C. for an effective amount of time to produce areaction product stream;

b) quenching the reaction product stream thereby resulting in a gaseousfraction, a liquid fraction and a solids fraction;

c) collecting at least a portion of the solids fraction;

d) passing the gaseous and liquid fractions to a separation zone whereinthe gaseous fraction is separated from the liquid fraction;

e) collecting the gaseous fraction for further use;

f) passing at least a portion of the liquid fraction and an effectiveamount of superheated steam to a reforming zone operated at atemperature of about 850° C. to about 1200° C. and a pressure form about3 psig to about 500 psig wherein said liquid fraction is reformed toproduce a synthetic gaseous product comprised of hydrogen, carbonmonoxide, carbon dioxide, and methane, which synthetic gaseous productstream is at an elevated temperature;

g) passing said synthetic gaseous product stream at an elevatedtemperature to a heat recovery zone wherein its temperature issubstantially lowered;

h) passing said lowered temperature synthetic gaseous product stream toa solids recovery zone wherein substantially all remaining solids areremoved;

i) passing said synthetic gaseous product stream having a reduced amountof solids to an organics removal zone wherein substantially anyremaining organic material is removed by contact with an organic liquidin which the organic material is at least partially soluble;

j) passing said synthetic gaseous product stream from said organicsremoval zone to an acid gas removal zone wherein substantially all acidgases are removed;

k) passing said synthetic gaseous product stream from said acid gasremoval zone to a methanation process unit containing at least onemethanation catalyst and operated at methanation process conditionsthereby resulting in a product stream comprised predominantly ofmethane.

In a preferred embodiment there is a water wash step between before theorganic removal step wherein the synthetic gaseous product stream ispassed countercurrent to a stream of water to remove any remainingsolids.

In another preferred embodiment the carbonaceous material is selectedfrom the group consisting of wood and dried distillers grains.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 hereof is a generalized flow scheme of a preferred embodiment ofthe present invention wherein a carbonaceous material, such as woodchips, are pryolyzed to produce a pyrolysis oil, which is then reformedto produce a syngas, which is then sent through various clean-up stepsthen to a methanation unit to produce synthetic natural gas.

DETAILED DESCRIPTION OF THE INVENTION

The present invention is directed to the production of synthetic naturalgas (predominantly methane) from carbonaceous materials, preferablybiomass materials. Synthetic natural gas, also sometimes called “greengas” is a renewable gas from biomass with natural gas specifications.Therefore, it can be transported through the existing gasinfrastructure, substituting for natural gas in all existingapplications. Another advantage of green gas is that is carbon neutral.That is, using biomass as an energy supply will typically not result ina net CO₂ emission since its source can be replanted and uses CO₂ fromthe atmosphere during its growth period.

While this invention is applicable to a broad range of carbonaceousfeedstocks including the traditional naturally occurring solid fossilfuels such as coal, peat, lignite, tar sands, and bitumen from oilshale, the preferred feedstocks for use in the present invention arebiomass feedstocks Non-limiting examples of biomass feedstocks suitablefor being converted in accordance with the present invention includetrees such as red cedar, southern pine, hardwoods such as oak, cedar,maple and ash, as well as bagasse, rice hulls, rice straw, kennaf, oldrailroad ties, dried distiller grains, corn stalks and cobs and straw.Cellulosic materials are the more preferred biomass feedstocks, withwood and dried distillers grains being the most preferred. Biomass istypically comprised of three major components: cellulose, hemicelluloseand lignin. Cellulose is a straight and relatively stiff molecule with apolymerization degree of approximately 10,000 glucose units (C₆ sugar).Hemicellulose are polymers built of C₅ and C₆ sugars with apolymerization degree of about 200 glucose units. Both cellulose andhemicellulose can be vaporized with negligible char formation attemperatures above about 500° C. On the other hand, lignin is a threedimensional branched polymer composed of phenolic units. Due to thearomatic content of lignin, it degrades slowly on heating andcontributes to a major fraction of undesirable char formation. Inaddition to the major cell wall composition of cellulose, hemicelluloseand lignin, biomass often contains varying amounts of species called“extractives”. These extractives, which are soluble in polar ornon-polar solvents, are comprised of terpenes, fatty acids, aromaticcompounds and volatile oil.

In most instances the carbonaceous mateials used in the practice of thepresent invention will be found in a form in which the particles are toolarge for conducting through the tubes of the pyrolysis unit. Thus, itwill usually be necessary to grind the carbonaceous material to aneffective size. In this case, the carbonaceous material is ground,otherwise reduced in size, to a suitable size of about 1/32 inch toabout 1 inch, preferably from about 1/16 inch to about ½ inch, and morepreferably from about ⅛ inch to about ¼ inch. Grinding techniques arewell know and varied, thus any suitable grinding technique and equipmentcan be used for the particular carbonaceous material being converted.

The type of pyrolysis preferred for use in the practice of the presentinvention is known as “fast pyrolysis” which is a thermal decompositionprocess that occurs at moderate temperatures with a high heat transferrate to the carbonaceous particles and a short hot vapor residence timein the reaction zone. Several conventional reactor configurations havebeen used in the art, such as bubbling fluid beds, circulating andtransported beds, vortex or cyclonic reactors, and ablative reactors.While all of these reactors have their advantages they are all facedwith limitations, such as the tendency of fluid bed reactors to producemore gas and coke then the desired pyrolysis oil, the preferredpyrolysis product of the present invention. The pyrolysis reactor of thepresent invention contains a plurality of vertically oriented straighttubes within the enclosed reactor vessel which is heated by use of asuitable heating device, such as one or more burners.

The pyrolysis of biomass as practiced by the present invention producesa liquid product, pyrolysis oil or bio-oil that can be readily storedand transported. Pyrolysis oil is a renewable liquid fuel can be usedfor production of chemicals and liquid fuels, or as herein for theproduction of synthetic natural gas. As previously mentioned, syntheticnatural gas is a very desirable product because it is derived from arenewable source and it can be used as a substitute for natural gas forall natural gas applications.

Generally, pyrolysis requires that a feedstock have less than about 15%moisture content, but there is an optimization between moisture contentand conversion process efficiency. The actual moisture content will varysomewhat depending on the commercial process equipment used. Since someof the biomass received for processing can have a moisture content fromabout 40 to 60% it will have to be dried before pyrolysis. Anyconventional drying technique can be used as long as the moisturecontent is lowered to less than about 15% when mixed with thesuperheated steam. For example, passive drying during summer storage canreduce the moisture content to about 30% or less. Active silo drying canreduce the moisture content down to about 12%. Drying can beaccomplished either by very simple means, such as near ambient, solardrying or by waste heat flows or by specifically designed dryersoperated on location. Also, commercial dryers are available in manyforms and most common are rotary kilns and shallow fluidized bed dryers.

This invention can be better understood with reference to the solefigure hereof. The carbonaceous feedstock is conducted via line 10 andsuperheated steam is conducted via line 12 to mixing zone Mix whereinthe two are sufficiently mixed before being conducted via line 14 intopyrolysis process unit P. The superheated steam, which will be at atemperature from about 315° C. to about 700° C. acts as both a source ofhydrogen as well as a transport medium. The amount of superheated steamto feedstock will be an effective amount. By effective amount we mean atleast that amount needed to provide sufficient transport of thefeedstock. That ratio of superheated steam to feedstock, on a volume tovolume basis, will typically be from about 0.2 to 2.5, preferably fromabout 0.3 to 1.0. The temperature conditions for the pyrolysis reactionwill be described later in detail. The steam is preferably introduced sothat the feedstock is diluted to the point where it can easily betransported through the reactor tubes. Fluidization will typicallyresult and can realize fluid pyrolysis by virtue of good contact amongsteam, feed polymers and heat decomposition products of carbonaceousmaterial liberated in the gas phase.

The mixture of steam and feedstock, which will be at a temperature ofabove its dew point of greater than about 230° C., is fed to thepyrolysis reactor P via line 14 into a flow divider FD where it isdistributed into the plurality of vertically oriented straight reactortubes of effective internal diameter and length within a metalcylindrical vessel of suitable size. Flow divider FD can be any suitabledesign that will divide the feedstock substantially equally among theplurality of reactor tubes. The reactor tubes for the pyrolysis reactorare straight instead of coiled because the residence time needs to bevery short in order to produce the maximum amount of oil without theproduction of an undesirable amount of gas. The temperature of themixture entering the pyrolysis unit will be at least about 230° C.Typical internal diameters for the pyrolysis reactor tubes will be fromabout 2 to about 4 inches, preferably from about 2.5 to about 3.5inches, and more preferably about 3 inches.

The feedstock passing though the pyrolysis reactor tubes is subjected tofast pyrolysis at temperatures from about 400° C. to about 650° C. andpressures from about 3 to 35 psig, preferably from about 5 psig to about35 psig. The residence time of the feedstock in the pyrolysis reactorwill be an effective residence time. By “effective residence time” wemean that amount of time that will result in the maximum yield of oilwithout excess gas make. Typically this effective amount of time forpurposes of this invention will be from about 0.2 to about 7 seconds,preferably from about 0.3 seconds to about 5 seconds. The heating ratewill be a relatively high heating rate of about 1,000° C. per second toabout 10,000° C. per second. The high heating rate in the pyrolysisreactor of the present invention, at temperatures below about 650° C.and with rapid quenching, causes the liquid intermediate products ofpyrolysis to condense before further reaction breaks down highermolecular weight species into gaseous products. The high reaction ratesalso minimize char formation, and under preferred conditionssubstantially no char is formed. At high maximum temperature, the majorproducts is gas, thus the need for the present process to operate at lowenough temperatures to maximize the production of pyrolysis oils.

Although the source of heat for the pyrolysis unit, as well as thereformer of the present invention, can be any suitable source, it ispreferred that the source of heat be one or more burners B located atbottom of the pyrolysis and reforming process unit. Fuel for the burnersB can be any suitable fuel. It is preferred that at least a portion ofthe fuel to the burners be obtained from the present process itself,such as the syngas produced in either the pyrolysis reactor or in thereformer. For example at least a portion of syngas stream 20 can bediverted via line 21 and used as a fuel to burners B. A portion of thesyngas stream 20 can also be combined with syngas stream of line 30.

Flue gas, which will typically be comprised of CO₂ and N₂ is exhaustedfrom the pyrolysis reactor via line 15 and the reaction products fromthe pyrolysis reactor are sent via line 16 to quench zone Q resulting ina mixture of liquid, gaseous and solid products. Most of the solids,which will typically be in the form of ash, will be collected fromquench zone Q via line 17. The liquid product will be in the form of apyrolysis oil and the gaseous product will be a syngas. The resultingliquid and gaseous products are conducted via line 18 to firstseparation zone Si wherein a syngas stream is separated from thepyrolysis oil and collected overhead via line 20 or a portion beingdiverted via line 21 to either or both of burners B. This syngas streamis comprised primarily of hydrogen, carbon dioxide, carbon monoxide, andmethane. The pyrolysis oil stream, which may contain some remnants ofchar and ash formed during pyrolysis, is conducted via line 22 toreformer R along with an effective amount of superheated steam via line23. It is preferred that reformer R contains a plurality of coiledreactor tubes within an enclosed reactor vessel heated by a suitableheating means, such as one or more burners.

At least a portion of the pyrolysis oil is converted to syngas inreformer R, which syngas is also composed primarily of hydrogen, carbondioxide, carbon monoxide and methane. The inlet temperature of thefeedstock and superheated steam entering reformer R will preferably beabout 200° C. The exit temperature of the product syngas leavingreformer R via line 24 will typically be from about 850° C. and 1200°C., preferably between about 900° C. and about 1000° C. At a temperatureof about 1100° C. and above and with a contact time of about 5 seconds,one obtains less than about 5 mole percent of methane and about 15 molepercent of CO₂, which is an undesirable result. Pressure in the reformeris not critical, but it will typically be at about 3 to 500 psig. Also,it is preferred that the residence time in the reformer be from about0.4 to about 1.5 seconds.

For any given feedstock, one can vary the proportions of hydrogen,carbon dioxide, carbon monoxide and methane that comprise the resultingsyngas product stream as a function of the contact time of the pyrolysisoil feedstock in the reformer, the exit temperature, the amount of steamintroduced, and to a lesser extent, pressure. Certain proportions ofsyngas components are better than others for producing synthetic naturalgas, thus conditions should be such as to maximize the production ofcarbon monoxide and methane at the expense of hydrogen.

Returning now to the Figure hereof flue gas is exhausted from thereformer via line 23 and the product syngas stream from reformer R isconducted via line 24 to heat recovery zone HR1 where it is preferredthat water be the heat exchange medium and that the water be passed aspreheated steam to one or both of the pyrolysis reactor P or reformer Rvia lines 25 where it is further heated to produce at least a portion ofthe superheated steam used for both units. Heat Recovery zone HR1 can beany suitable heat exchange device, such as the shell-and-tube typewherein water is used to remove heat from product stream 24. From heatrecovery zone HR1 the product syngas is passed via line 26 throughsecond separation zone S2 which contains a gas filtering means andpreferably a cyclone (not shown) and optionally a bag house (not shown)to remove at least a portion, preferably substantially all, of theremaining ash and other solid fines from the syngas. The filtered solidsare collected via line 28 for disposal.

The filtered syngas stream is then passed via line 30 to water wash zoneWW wherein it is conducted upward and countercurrent to down-flowingwater via line 31. The water wash zone preferably comprises a columnpacked with conventional packing material, such as copper tubing, pallrings, metal mesh or other such materials. The syngas passes upwardcountercurrent to down-flowing water which serves to further cool thesyngas stream to about ambient temperature, and to remove any remainingash that may not have been removed in second separation zone S2. Thewater washed syngas stream is then passed via line 32 to oil wash zoneOW where it is passed countercurrent to a down-flowing organic liquidstream to remove any organics present, such as benzene, toluene, xylene,or heavier hydrocarbon components via line 35 that may have beenproduced in the reformer. The down-flowing organic stream will be anyorganic stream in which the organic material being removed issubstantially soluble. It is preferred that the down-flowing organicstream be a hydrocarbon stream, more preferably a petroleum fraction.The preferred petroleum fractions are those boiling in naphtha todistillate boiling range, more preferably a C₁₆ to C₂₀ hydrocarbonstream, most preferably a C₁₈ hydrocarbon stream.

The resulting syngas stream is conducted via line 34 to acid gasscrubbing zone AGS wherein acidic gases, preferably CO₂ and H₂S areremoved. Any suitable acid gas treating technology can be used in thepractice of the present invention. Also, any suitable scrubbing agent,preferably a basic solution can be used in the acid gas scrubbing zoneAGS that will adsorb the desired level of acid gases from the vaporstream. It will be understood that it may be desirable to leave acertain amount of CO₂ in the scrubbed stream depending on the intendeduse of resulting methane product stream from the methanation unit. Forexample, if the methane product stream is to be introduced into anatural gas pipeline, no more than about 4 vol. % of CO₂ should beremain. If the methane product stream is to be used for the productionof methanol, then at least that stoichiometric amount of CO₂ needed toresult in the production of methanol should remaing. One suitable acidgas scrubbing technology is the use of an amine scrubber. Non-limitingexamples of such basic solutions are the amines, preferably diethanolamine, mono-ethanol amine, and the like. More preferred is diethanolamine. Another preferred acid gas scrubbing technology is the so-called“Rectisol Wash” which uses an organic solvent, typically methanol, atsubzero temperatures. The scrubbed stream can also be passed through oneor more guard beds (not shown) to remove catalyst poisoning impuritiessuch as sulfur, halides etc. The treated stream is passed via line 36from acid gas scrubbing zone AGS to methanation zone M. Methanation ofsyngas involves a reaction between carbon oxides, i.e. carbon monoxideand carbon dioxide, and hydrogen in the syngas to produce methane andwater, as follows:

CO+3H₂→CH₄+H₂O   (1)

CO₂+4H₂→CH₄+2H₂O   (2)

Methanation reactions (1) and (2) take place at temperatures of about300° C. to about 900° C. in methanation zone M which is preferablycomprised of two or more, more preferably three, reactors eachcontaining a suitable methanation catalyst. The methanation reaction isstrongly exothermic. Generally, the temperature increase in a typicalmethanator gas composition is about 74° C. for each 1% of carbonmonoxide converted and 60° C. for each 1% carbon dioxide converted.Because of the exothermic nature of methanation reactions (1) and (2),the temperature in the methanation reactor during methanation of syngashas to be controlled to prevent overheating of the reactor catalyst.Also high temperatures are undesirable from an equilibrium standpointand reduce the amount of conversion of syngas to methane since methaneformation is favored at lower temperatures. Formation of soot on thecatalyst is also a concern and may require the addition of water to thesyngas feedstock.

A preferred way to control heat during the methanation reaction is use aplurality of reactors with heat removed between each reactor. Thus,methanation zone M preferably comprises a series of three adiabaticmethanation reactors R1, R2 and R3. Each of these reactors is configuredto react carbon oxide and hydrogen contained in the syngas in thepresence of a suitable catalyst to produce methane and water, inaccordance with the reactions (1) and (2) set forth hereinabove. Each ofthe methanation reactors includes a catalyst capable of promotingmethanation reactions between carbon oxides and hydrogen in the syngasfeedstock. Any conventional methanation catalyst is suitable for use inthe practice of the present invention, although nickel catalysts aremost commonly used and the more preferred for this invention. Suchcatalysts are, especially those containing greater than 50% nickel, aregenerally stable against thermal and chemical sintering duringmethanation of undiluted syngas streams. Alternatively, other stablecatalysts that are active and selective towards methane may be used inthe methanation reactors.

As previously mentioned because the methanation reaction is stronglyexothermic, heat needs to be removed between reactors. Thus, heatrecover zones HR2 and HR3 are used to remove heat from the stream as itpassed from reactor R1 to reactor R2 and reactor R2 to reactor R3respectively. Any suitable exchange device can be used, preferably ashell-and-tube type wherein water can be used to remove heat from theproduct stream. The water can then be recycled to one or both of 12 and23 where it can be further heated to produce superheated steam. As canbe appreciated from the above and as shown in the examples discussedbelow, the inlet and outlet temperatures of the streams entering andexiting methanation reactors R1-R3 can be controlled by varying thepercentage of syngas being delivered to each of the reactors as well ashow much heat is exchanged by heat exchangers HR2 and HR3. Typically,the inlet temperature of reactors R1 and R2 will be from about 400° F.to about 450° F. with an outlet temperature of about 500° F. to about800° F. The third reactor, which will operate at a lower temperaturethan that of reactors R1 and R2 will have an inlet temperature of about400° F. and an outlet temperature of about 500° F.

In a preferred embodiment of the present invention, the step ofrecovering at least a part of generated heat and/or at least a part ofwaste heat in the regeneration zone and effectively utilizing therecovered heat is further provided. The recovered heat can beeffectively utilized, for example, for drying and heating of the biomassfeedstock and the generation of steam as the gasifying agent.

The product stream from the methanation unit will be comprisedpredominantly of methane. That is, it will contain at least about 75vol. %, preferably at least about 85 vol. %, and more preferably atleast about 95 vol. % methane. If the methane product stream is to beintroduced into a natural gas pipeline, then it must meet thespecification requirements for the pipeline. Such a specification formost pipelines, with respect to CO₂ content will be less than about 4volume percent. If the methane product stream is to be used for theproduction of methanol, then higher amounts of CO₂ will be required. Theproduct methane stream is preferably introduced into a natural gaspipeline and utilized at any downstream facility. One such facility ifpreferably a plant that converts the methane to syngas then to otherproducts, such as alcohols, transportation fuels, or lubricant basestocks. If it is desired to produce syngas from the methane produced inthe methanation unit M, then any suitable process can be used thatconvert methane or natural gas to syngas. Preferred methods includesteam reforming and partial oxidation. More preferred is steamreforming. Steam reforming of methane is a highly endothermic processand involves following reactions:

Main reaction

CH₄+H₂O→CO+3H₂ −54.2 Kcal per mole of CH₄ at about 800° C. to about 900°C.

Side reaction

CO+H₂O→CO₂+H₂ +8.0 kcal per mole of CO at about 800° C. to about 900° C.

CO₂ reforming of methane: It is also a highly endothermic process andinvolves the following reactions:

Main reaction

CH₄+CO→2CO+2H₂ −62.2 kcal per mole of CH₄ at about 800° C. to about 900°C.

Side reaction: Reverse water gas shift reaction

CO₂+H₂→CO+H₂O −8.0 kcal per mole of CO₂ at about 800° C. to about 900°C.

The steam reformer will preferably be one similar to reformer R hereof,which is a coiled tubular reactor. Preferred steam reforming catalystsare nickel containing catalysts, particularly nickel (with or withoutother elements) supported on alumina or other refractory materials, inthe above catalytic processes for conversion of methane (or natural gas)to syngas is also well known in the prior art. Kirk and Othmer,Encyclopedia of Chemical Technology, 3rd Ed., 1990, vol. 12, p. 951;Ullmann's Encyclopedia of Industrial Chemistry, 5th Ed., 1989, vol. A12,pp. 186 and 202; U.S. Pat. No. 2,942,958 (1960); U.S. Pat. No. 4,877,550(1989); U.S. Pat. No. 4,888,131 (1989); EP 0 084 273 A2 (1983); EP 0 303438 A2 (1989); and Dissanayske et al., Journal of Catalysis, vol. 132,p. 117 (1991).

The catalytic steam reforming of methane, or natural gas, to syngas is awell established technology practiced for commercial production ofhydrogen, carbon monoxide and syngas (i.e., a mixture of hydrogen andcarbon monoxide). In this process, hydrocarbon feed is converted to amixture of H₂, CO and CO₂ by reacting hydrocarbons with steam over asupported nickel catalyst such as NiO supported on alumina at elevatedtemperature (850° C. to 1000° C.) and pressure (10-40 atm) and at steamto carbon mole ratio of 2-5 and gas hourly space velocity of about5000-8000 per hour.

This process is highly endothermic and hence it is carried out in anumber of parallel tubes packed with a catalyst and externally heated byflue gas to a temperature of 980° C. to about 1040° C. (Kirk and Othmer,Encyclopedia of chemical Technology, 3rd, Ed., 1990, vol. 12, p. 951,Ullmann's Encyclopedia of Industrial Chemistry, 5th Ed., 1989, vol. A12,p. 186).

1. A process for converting carbonaceous material to synthetic natural gas, which process comprising: a) feeding said carbonaceous material and an effective amount of superheated steam through a plurality of vertically oriented tubes in a pyrolysis furnace, which tubes are at a temperature of about 400° C. to about 650° C. for an effective amount of time to produce a reaction product stream; b) quenching the reaction product stream thereby resulting in a gaseous fraction, a liquid fraction and a solids fraction; c) collecting at least a portion of the solids fraction; d) passing the gaseous and liquid fractions of the reaction product stream to a separation zone wherein the gaseous fraction is separated from the liquid fraction; e) collecting the gaseous fraction for further use; f) passing at least a portion of the liquid fraction and an effective amount of superheated steam to a reforming zone operated at a temperature of about 850° C. to about 1000° C. and a pressure form about 3 psig to about 500 psig wherein said liquid fraction is reformed to produce a synthetic gaseous product comprised of hydrogen, carbon monoxide, carbon dioxide, and methane, which synthetic gaseous product stream is at an elevated temperature; g) passing said synthetic gaseous product stream at an elevated temperature to a heat recovery zone wherein its temperature is substantially lowered; h) passing said lowered temperature synthetic gaseous product stream to a solids recovery zone wherein substantially all remaining solids are removed; i) passing said synthetic gaseous product stream having a reduced amount of solids to an organics removal zone wherein substantially any remaining organic material is removed by contact with an organic liquid in which the organic material is at least partially soluble; j) passing said synthetic gaseous product stream from said organics removal zone to an acid gas removal zone wherein substantially all acid gases are removed; k) passing said synthetic gaseous product stream from said acid gas removal zone to a methanation process unit containing at least one methanation catalyst and operated at methanation process conditions thereby resulting in a product stream comprised predominantly of methane.
 2. The process of claim 1 wherein the carbonaceous material is a source of fossil fuels selected from the group consisting of coal, peat, lignite, tar sands, and bitumen from oil shale.
 3. The process of claim 1 wherein the carbonaceous material is a biomass material.
 4. The process of claim 3 wherein the biomass material is a cellulosic material.
 5. The process of claim 4 wherein the cellulosic material is selected from the group consisting of wood, bagasse, rice hulls, rice straw, kennaf, old railroad ties, dried distiller grains, corn stalks and cobs and straw.
 6. The process of claim 5 wherein the cellulosic material is selected from wood and dried distiller grains.
 7. The process of claim 1 wherein the carbonaceous material is dried to a moisture content of less than or equal to about 15% by weight before pyrolysis.
 8. The process of claim 1 wherein the carbonaceous material is with the size range of about 1/16 inch to about ½ inch.
 9. The process of claim 1 wherein the gaseous product collected from the separation zone is a fuel gas a portion of which is used to fuel the pyrolysis unit, the reforming zone, or both.
 10. The process of claim 1 wherein the heat recovery zone uses water to recover heat and wherein at least a portion of the heated water is used as preheated steam to the pyrolysis unit, the reforming zone, or both.
 11. The process of claim 1 wherein the scrubbing agent used in the acid gas removal zone is selected from the group consisting of alcohols and amines.
 12. The process of claim 11 wherein the scrubbing agent is an alcohol.
 13. The process of claim 12 wherein the alcohol is methanol.
 14. The process of claim 11 wherein the amine is selected from the group consisting of diethanol amine and mono-ethanol amine.
 15. The process of claim 14 wherein the amine is diethanol amine.
 16. The process of claim 1 wherein the methanation zone contains three reactors in series and wherein heat is removed from the stream passing from the first reactor and the second reactor.
 17. The process of claim 1 wherein at least a portion of the methane produced in the methanation unit is introduced into a natural gas pipeline.
 18. The process of claim 17 wherein methane is removed from a pipeline and converted to a syngas.
 19. The process of claim 1 wherein prior to organic removal step (j) the synthetic gaseous product stream is subjected to a water wash wherein is flowed countercurrent to a stream of water to remove any remaining solids material. 